# Abnormal Cortical Thickness Development in Young Adults With Heavy Cannabis Use: A Longitudinal Study

## TL;DR

This study finds that heavy cannabis use in young adults is linked to reduced cortical thickness in the left lateral orbitofrontal cortex over three years, potentially affecting decision-making and addictive behaviors.

## Contribution

The study provides longitudinal evidence linking heavy cannabis use to structural brain changes in the left lateral orbitofrontal cortex.

## Key findings

- Heavy cannabis users showed significant cortical thickness reduction in the left lateral orbitofrontal cortex after three years.
- Cortical thickness in the left lateral orbitofrontal cortex correlated with cannabis use disorder severity scores.
- No baseline cortical differences were found between heavy cannabis users and controls, but differences emerged at follow-up.

## Abstract

Cannabis is one of the most commonly used illicit drugs worldwide, with its prolonged use potentially leading to various cognitive impairments and brain structural changes. However, current research on the dynamic changes in cortical thickness (CT) related to cannabis use remains limited, especially regarding the relationship between the severity of cannabis use and CT changes in heavy cannabis use (HCU). This study employed a longitudinal design to investigate CT changes in young adults with HCU from baseline (BL) to 3‐year follow‐up (FU). The results showed a significant group effect in the left lateral orbitofrontal cortex (OFC), and a significant time effect revealed CT changes in several brain regions, including the left lateral frontal cortex, bilateral medial frontal cortex, bilateral posterior cingulate cortex and bilateral insula. Simple effects analysis further demonstrated that the CT of left lateral OFC in young adults with HCU decreased significantly at FU compared with their BL and was also lower than control group at FU. Furthermore, a significant positive correlation was observed between the total score of Cannabis Use Disorders Identification Test at FU and the CT of left lateral OFC. These findings suggest that prolonged cannabis use may disrupt the structural integrity of the left lateral OFC, impairing decision‐making, impulse control and emotional processing, thereby exacerbating addictive behaviours. This study provides key evidence for understanding the neural mechanisms underlying cannabis addiction.

At BL, there was no significant difference in the CT of the left lateral OFC between the two groups. However, at FU, young adults with HCU exhibited significantly lower CT in the left OFC compared to their own BL and to the HC group at the same time point. Moreover, at FU, there was a significant correlation between the CUDIT total score and the CT of the left lateral OFC.